Calendar and Time
Life is not, and preferably need not necessarily have to be, any sort of
Classification of time into calendar of any type has been made for conveniences of reference point for recording and recollecting.
Physically, human body works best when and if it tunes to external natural climate ( or one has to create energy guzzling devices to counter the effect of some extreme climate conditions).
Psychologically, human beings work through prompts, pleasures , pain etc all sorts of emotional actions and reactions with varying degrees of intensities emanating from two major human emotions Love and Fear.
So, any calendar, be it Gregorian or otherwise is mostly on approximations because the study of whole gamut of astronomy is still a work in progress and a science which prefers to evolve and engage with any new emerging clarifications or corrections.
Therefore, no slice of Time made by any civilization with all its Calendared celebration of festivities can claim with axiomatic certitude that this is the best or even a better approximation than the rest.
Besides, the science of astrology along with astronomy, has aided the world to have some commonalities (to the vast geographical space of planet Earth to refer to MOMENTS OF LIFE to mathematically definable slices of TIME) Gregorian calendar too has astrological factors embedded in it.
There are, at least a few hundred calendars, and in the interest of and for the convenience of smoother functioning of majority of activities in many places, as in the case of languages. so do in calendars too the number of those in active usage has reduced.
The lesser number of languages has enabled the world to function with greater ease, so do calendar.
It does not mean any particular language or calendar is great or better than the rest.
Evolution in its stride decides what needs to be compromised and what needs to be the ' trade off ' for convenience and comfort of living.
Time is an eternal puzzle because it is an abstract created for convenience used for measurement, for classification etc and therefore eludes all sorts of definition.